Coating articles with molybdenum



June 20, 1950 c, c, MA ETAL 2,512,141

COATING ARTICLES WITH MOLYBDENUM Filed June 14, 1945 04' yep/wwf PMP/v6 lNvENTORS NWO] mm ATTORN EY Patented June 2Q, 1950 UNITED PATENT OFFICE house Electric Corporation, East Pittsburgh, Pa., aicorporation of Pennsylvania Application June 14, 1945, Serial.No.f599,332

solairms. (Ciani-37) This invention relates to electroplating zand more particularly to such a process for depositing molybdenum on articles formed rof basemetal. l

The principal object of ourinvention, generally ous solutions on conductive surfacespf articles.

Another object of our invention is `toprovide metal articles coated with pure or v.uncontaminated molybdenum, byrst plating hydrated molybdenum sesquioxide from a molybdenumlsalt 10 solution, and then heating the plated article in a suitable atmosphere to reduce the plating .to

metallic molybdenum. y y

A further object of our invention is to provide a process for plating molybdenum throughouta 15 wide range of molybdenumsalt concentrations, pI-l, current densities, and bath temperatures.

A still further object of our invention is to electroplate metal articles With-la coating consisting essentially of molybdenum sesquioxide and 20 then reduce to metal said coating inhydrogen, carbon monoxide, or other reducing atmosphere, by heating therein to a temperature fof between '700 C. and 1200 C.

An additional object of our invention is `tol provide a satisfactory bathfrom which-a molybdenum compound may be depositedas a rmlyadherent film on the surface of ,a `metal article.

Other objects and advantages oi'the invention of almostiany strength,r dilute hydrofluoric acid, or dilute sulphuric acid. Although inferior to tungsten in hardness and .resistance to chemical corrosion, it is superior in'ductility Aand workconsidered, is to deposit molybdenum `from aque- 5 ability. On4 account of its several valuable characteristics `from la, standpoint of Vresistance to chemical corrosion, erosion, and-abrasion, molybdenum isuseful asa protective coating for base metals.

It has been attempted todeposit molybdenum from aqueous lsalt solutions, but because of .the chemical reactivity between the nascent molybdenum atoms .and those of water, and the relative insolubility and stability of molybdenum sesquioxide, the latter in a hydrated condition (MozOaHzO) is `deposited on a cathode from an aqueous molybdenum salt solution, rather than metallicv molybdenum. We have found that this sesquioxide is deposited not only from alkaline molybdate solutions but also from weakly acid solutions, that is, within a pI-Irange of 4 to 9.

Referring to the drawing in detail, and rst considering Fig. 1, it will be seen that the ferrous or other base metal is vplated with hydrated molybdenum vsesquioxide (MozOaI-IzO) in an acid or alkaline molybdenum salt solution. Examples of such solutions which 4have been used, and the current employed, as well as the results obtained,

y are given in the .following table:

Base Size of Thickness oi soiutionused cgfs Cafsn AMetal .plata the plate, y. n Plated inches inches 15% ammonium molybdate solution 5 2 N ickeL.-- x 3 0.004 (approx.). 15%'ammonium'molybdate' solution, modified; 5 4 do.- 1A x 3 0.004 (approx.).

byiaceticacid to pH 5; l 15 0 sodium molybdate solutlon. -1 .5 5 ---do---- M x-3 v0.003 (approx.). 10 sodium molybdate solution,'heated to 70 C. 4 5 'Copper. 1 x 3 0.003 (approx).

beforeelectrolyzing. l. 20% sodiumvmolybdate solution 5 5 fln 1 x 3 0.003 (approx.). 10% sodiuminolybdatesolution... '5 4 Iron l x 3 0.003 (approx.).

will become apparent as the description proceeds.`

Referring to the drawing:

Fig. 1 is a flow diagram illustrating howiour y invention may be practiced.

Fig. 2 isa perspective view Vof axproduct of .our

process.

As is generally known, molybdenum isnot alti room temperatures attacked-by hydrochloric acid I0:

It will 'therefore `be seen that we may deposit the ,sesquioxide :on v almostany usual base metal, except one attacked by the solution used in the plating operation. Usable base metals, therefore, obviously fin'clude molybdenum. The solution may befrom 10% 130.20%- of an alkali molybdate, or suchf'solution ymay Abe a'cidulated at least up topi-I5 Wlthca weakacid, such as acetic. We

may also plate the sesquioxide from an acid bath formed by dissolving molybdenum trioxide, say 100 grams, in a weak acid such as perchloric, or sulphuric or hydrochloric, diluted in the proportion of 50 to l5 grams of acid per liter of water, thereby obtaining the perchlorate, the sulphate or the chloride of molybdenum, as the case may be. Strong acid is to be avoided because of its attack on the metal to be plated. The current density, whether the bath be alkaline or acid, to produce an adherent coating is desirably low, that is, between .2 and 1 ampere per sq. inch of cathode surface.

When the surface of the cathode becomes com pletely coated with the black molybdenum sesquioxide, further plating appears to stop and hydrogen is evolved. This processhasbeeniound to take from to 20 minutes -depending on the current density employed. Thicker coatingsl are obtainable by dehydrating and reducingthe ses-N quioxide to metallic molybdenum, by heating to between 700 and 1200 C. in a reducing" atmosf phere, such as hydrogen, carbon monoxide`, wateri gas, or Endogas, which is a partially combusted mixture of air and city gas, as deiined'in'the Rennie application, Ser. No. 471,604, filed January 7, 1943, 110W Patent No. 2,402,084, 'datedJune 141,'

1946, before continuing the process.

If a strongly-reducing gas, suchas hydrogen, is employed, the temperature for eifecting the reduction may be lower, that is, between 700 and 1000 C. than ifa more weakly reducing gas, such as Endogas, is employed in which'case a tem' perature between 1000 and 1200 C. is desirably employed. However, reduction starts r to ltake place at temperatures above 600 C.,-but the higher the temperature the quicker thefreducing action. y

If the base metal on which the plating is applied is steel or other carbon-containing-material;

it is desirable to use a non-`decarbonizing atmos phere, such as carbon monoxide, Endogas, or'

other reducing atmosphere which is notf t'oorrich in hydrogen, as Vpure hydrogen and high concen-` trations thereof tend to decarbonize'such material by combining with'the carbon content thereof and producing hydrocarbons;

After the iirst oxide plafng has beenjreduced to metal, the process of plating andreductiorr may be repeated any number of times to build' up the plating to thedesired thickness.: Inother words, the Sesquioxide may'be plated ori-metallic molybdenum, and if the base metal-is all molyb denum the plated or built-up' article,y includingthe reduced sesquicxide, may then,A ofcourse, -beI handled like solid molybdenum produced in .a

customary manner. After the plating has been built up to the, desired thicknessthe article may, if desired, be annealed in a reducing o-r inert atmosphere. Fig. 2 illustrates such van article comprising a base lmetal having a plating of' molybdenum on its surface.

From the foregoing disclosure, it will be seen.

that our invention involves two distinct discoveries, iirst a method for plating a firmly-adherent coating of molybdenum sesquioxide from anacid or alkaline molybdenum salt solution within a wide range of molybdenum.concentrations, hydrogen ion concentrations, current densities, 'and' bath temperaturesand,second, how to change'. this sesquioxide coating to` fa likewisesfirmly-V adherent coating of metallic molybdenum. 'Ourl process results in an adherent coating. of: molyb denum, and may begpracticedusing ,solutions of; high conductivitiesA at temperatures between about and 100 C. If a reducing atmosphere, in which hydrogen not too concentrated, is employed, the base metal is not decarburized.

A general schedule for the production of molybdenum plate would therefore be as follows:

1. Plate molybdenum sesquioxide on the metal or other article having a conductive surface, from an acid or alkaline solution, using a pH between 4 and 12. The temperature of the bath does not seem to matter, provided it is between usual room temperatures and 100 C.

2. The black sesquioxide on the surface is then reduced either, in hydrogen between 700 and 1000 C., if there is no fear of l"tzlecarburation, or 15 in Endogas or other more weakly reducing 'L l agent between 1000 and 1200 C. The article after reduction is cooled below 100 C. before it is taken from the furnace in order to avoid sub- `sequent reoxidation.

, k3. Plate another coating by repeating the processes of the preceding paragraphs l and 2.

' 4. Repeat the process of paragraphs 1 and 2 L. until the desired thickness of molybdenum plate is obtained.

5. Anneal, if desired, in a vacuum, an inert gas, o r a reducing gas.

Although a preferred embodiment of our invention has been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

We claim: {1 .UThe method of coating a conductive surface oan article of meta1,"not attacked by weak acids and alkalis, with metallic molybdenum, compris- King` forming a 10% to 20% aqueous solution, i within a pI-I range of 4 to 12, of a compound of molybdenum selected from the group consisting of the alkali molybdates and the perchlorate, the sulphate, and the chloride of molybdenum, plac- 40 ing said article in said solution, depositing a plating consisting essentially of molybdenum sesquioxide thereon by making it the cathode, and then heating said plated article to a temperature above 600 C. in a gaseous reducing atmosphere to reduce the plated compound to 'f' metallic molybdenum.

2. The method of coating an article of metal, not attacked by weakv acids and alkalis, with metallic molybdenum, comprising forming a 10% 5 0 to 20% aqueous solution, within a pH range of 4to 12, of a compound of molybdenum selected from the group consisting of the alkali molybdates and the perchlorate, the sulphate, and the chlorideof molybdenum, placing said article therein,

depositing a 'plating consisting essentially of Vmolybdenum sesquioxide thereon by making it the cathode, and heating said plated article to a temperature between about 700 and 1200 C.

in a gaseous reducing atmosphere to reduce the plating to metallic molybdenum.

A 3.2 The methodfof fcoating an article of metal,

not attacked by weak acids and alkalis, with s metallic molybdenum, comprising forming a from 10% to 20% alkali molybdate aqueous solution,

V05 'within a pHrangefof 4 to 12, placing said article nl therein and depositing a plating consisting essentially of molybdenum sesquioxide thereon by passing a current between it as a cathode and an anode in said solution, with a current density 70 between .2 and 1 ampere per sq. in., removing said article from said solutionyand heating it tol a temperature above 600 C. in a gaseous reducing atmosphere to reduce the plating to metallic molybdenum.

1,51 .4. The method ofz`coatng an article of metal,`

not attacked by weak acids and alkalis, with metallic molybdenum, comprising forming a to 20% aqueous solution, within a pH range of 4 to 12, o-f a compound of molybdenum selected from the group consisting of the alkali molybdates and the perchlorate, the sulphate, and the chloride of molybdenum, placing said article in said solution, and depositing a plating consisting essentially of molybdenum sesquioxide thereon by making it the cathode therein, removing said article, heating it to a temperature above 600 C. in a gaseous reducing atmosphere to reduce the plating to metallic molybdenum, and annealing in a protective atmosphere.

5. The method of coating a carbon-containing article of metal, not attacked by weak acids and alkalis, in which decarburization is undesirable, with metallic molybdenum, comprising forming a 10% to 20% aqueous solution, Within a pH range of 4 to l2, of a compound of molybdenum selected from the group consisting of the alkali molybdates and the perchlorate, the sulphate, and the chloride of molybdenum, placing said article in said solution, and depositing a plating of molybdenum sesquioxide thereon by making it the cathode therein, removing said article, heating it to a temperature above 600 C. in a gaseous reducing atmosphere not containing a large enough proportion of hydrogen to decarburize the metal article, to reduce the plating to metallic molybdenum, and annealing in a protective atmosphere to regain the desired properties of the original uncoated article.

6. The method of coating an article of metal, not attacked by weak acids and alkalis, with metallic molybdenum. comprising forming a 10% to 20% alkali molybdate aqueous solution, within a. pH range of 4 to 12, placing said article therein, depositing a plating of hydrated molybdenum sesquioxide thereon by making it the cathode, and then heating said plated article to a temperature above 600 C. in a gaseous reducing atmosphere to remove the oxygen from the plating and leave metallic molybdenum.

7. The method of coating an article of metal, not attacked by weak acids and alkalis, with metallic molybdenum, comprising forming a 10% to 20% aqueous solution, within a pH range of 4 to 12, of an alkali molybdate, heating said solution, placing said article therein, depositing a plating of hydrated molybdenum sesquioxide thereon by making it the cathode, removing said article, and heating it to a temperature between about 700 and 1200 C. in a gaseous reducing 65 atmosphere to dehydrate and remove the oxygen from said plating, leaving metallic molybdenum on said article.

8. The method of coating an article of metal, not attacked by weak acids and alkalis, with metallic molybdenum comprising forming a 10% to 20% alkali molybdate aqueous solution, within a pH range of 4 to 12, placing said article therein, depositing a plating consisting of hydrated molybdenum sesquioxide thereon by passing a current between it as a cathode and an anode in said solution, removing said article, and heating it in a hydrogen atmosphere between about 700 and 1000 C. to dehydrate and reduce the plating to metallic molybdenum.

9. The method of coating an article of metal, not attacked by weak acids and alkalis, with metallic molybdenum comprising forming a 10% to 20% alkali molybdate aqueous solution, within a pH range of 4 to 12, placing said article therein, depositing a plating of hydrated molybdenum sesquioxide thereon by causing a current to ilow between it as a cathode and an anode in said solution, removing said article, and heating it in a gaseous reducing atmosphere relatively low in hydrogen to a temperature between about 1000* and 1200 C. to dehydrate and reduce the plating to metallic molybdenum.

CHUK CHING MA. MARTIN WM. OFFINGER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,019,546 Theis Nov. 5, 1935 2,059,053 Stareck Oct. 27, 1936 2,081,121 Stareck May 18, 1937 2,116,927 Germer May 10, 1938 2,313,456 Stareck Mar. 9, 1943 2,351,639 Schweikher June 20, 1944 2,380,044 I-Ioiman July 10, 1945 2,385,843 Rennie Oct. 2, 1945 2,398,114 Rennie Apr. 9, 1946 2,420,886 Laioon, Jr. May 20, 1947 FOREIGN PATENTS Number Country Date 361,560 Great Britain Nov. 26, 1931 582,528 Germany May 22, 1934 OTHER REFERENCES Transactions of the Electrochemical Society, volume (1936), page 423. 

1. THE METHOD OF COATING A CONDUCTIVE SURFACE OF AN ARTICLE OF METAL, NOT ATTACKED BY WEAK ACIDS AND ALKALIS, WITH METALLIC MOLYBDENUM, COMPRISINFG FORMING A 10% TO 20% AQUEOUS SOLUTION, WITHIN A PH RANGE OF 4 TO 12, OF A COMPOUND OF MOLYBDENUM SELECTED FROM THE GROUP CONSISTING OF THE ALKALI MOLYBDATES AND THE PERCHIORATE, THE SULPHATE, AND THE CHLORIDE OF MOLYBDENUM, PLACING SAID ARTICLE IN SAID SOLUTION DEPOSITING A 